Spawner Update: Coho Spawning Draws to a Close

The 15+ inches of rain we received in December was good for coho salmon seeking to migrate up into San Geronimo Creek and was also good for MMWD’s water supply. Our reservoirs reached capacity and Kent Lake began spilling into Lagunitas Creek on December 29. This week stream flows receded enough to allow MMWD and National Park Service biologists to conduct spawner surveys through eight miles of the creek. Unfortunately only two coho and one redd were found during those surveys. Last week only one coho and two redds were found in San Geronimo Creek and Devil’s Gulch. We had hoped that the late-December rains would encourage a second peak in coho spawning, but spawning activity has been steadily declining since peaking on December 7. It appears that the coho run is essentially over for the 2010-11 season.

Our survey numbers are still preliminary, and a few coho may yet spawn, but it’s probably not too early to do a postmortem on this year’s coho salmon run. For the season, we recorded 78 coho redds and 145 live coho. We saw 32 redds in Lagunitas Creek, 40 in San Geronimo Creek and six in Devil’s Gulch. In addition, surveyors with the Salmon Protection and Watershed Network (SPAWN) observed seven coho and two redds in the tributaries to San Geronimo Creek. While the coho run was larger than the disastrous runs of the previous two seasons, it was just over half the size of the previous generation, which spawned three years ago. The run will go down as the third smallest coho run recorded in the Lagunitas Creek watershed. On a positive note, 60 percent of this season’s redds are located out of the main stem of Lagunitas Creek and the eggs they contain are less likely to be washed away by winter floods. The next step in the coho population rebound will hopefully involve thousands of coho fry emerging throughout the watershed.

Some of you may remember my observation early in the spawning season of an unusually high percentage of coho jacks, which are small male salmon. I was encouraged because large numbers of jacks can foreshadow a large run of salmon in the following year. For the rest of the season jacks continued to make up a fairly high percentage of the coho run, comprising 35 percent of all the coho spawners seen. The 44 jacks we counted this year may predict a coho run of somewhere in the neighborhood of 300 spawners next year, based on the last 14 years of data. This would still be a below-average coho run, but it would be a big improvement from where we are now.

I’ve heard a few reports of steelhead spawners in the watershed and we’ve gotten glimpses of fish that may have been steelhead. Over the next two months I’ll be writing periodic updates on the status of this next run of salmonids.